Identifier

Author

Degree

Doctor of Philosophy (PhD)

Department

Renewable Natural Resources

Document Type

Dissertation

Abstract

A suitable foraging habitat model based on prey density, biomass, and energy values in varying hydrologic conditions can provide an objective quantifiable method to assess habitat conditions for the Whooping Crane (Grus americana). Nekton and macroinvertebrates are considered the important prey sources in Whooping Crane's diet at different times. This study focuses on the understanding of habitat relationships of nekton and macroinvertebrate assemblage in the Chenier Plain to provide a foundation for the development for foraging suitability models for the reintroduced Whooping Crane. In this dissertation, in a laboratory study I experimentally examined the effect of salinity on the survival of dominant macroinvertebrates in freshwater marsh (i.e., Procambarus clarkii Girard, Cambarellus puer Hobbs, Libellulidae, Dytiscidae). In addition, I compared nekton and aquatic macroinvertebrate assemblages in freshwater, brackish and saline marshes of the Chenier Plain. In the laboratory experiment, to determine survival rate, a series of 45 cm x 30 cm x 15 cm plastic trays were filled with water of six salinities (i.e., 0.6, 7.2, 13.5, 19.4, 25.1, and 30.7 g/lTDS) both with and without prey for 28 days. At the lower threshold, low salinities (i.e.,¡Ü 0.6 g/lTDS) allowed species to survive even without food. Above the upper threshold, however, high salinities (i.e.,¡Ý 25.1g/lTDS) killed species whether they had food or not. Survival of all species was affected by salinity but upper and lower thresholds existed for each species. In the field studies, I measured the effects of hydrologic connectivity on several environmental variables and their combined effect on several nekton community metrics. I collected 31,011nekton of 42 taxa from 540 seasonal samples with a throw trap and minnow traps. Nekton density of brackish ponds was higher than saline ponds but freshwater ponds did not statistically differ from brackish and saline ponds. However, nekton biomass of brackish and saline ponds was greater than freshwater ponds. Nekton community diversity of freshwater ponds had the highest diversity. Nekton community composition appeared to be structured by individual species responses to the salinity gradient as well as pond habitat attributes (submerged aquatic vegetation coverage, dissolved oxygen, hydrologic connectivity). To determine the effects of hydrologic connectivity and environmental variables on aquatic macroinvertebrate community metrics, I collected 32,130 aquatic macroinvertebrates from 52 taxa from 252 monthly sweep net samples. A total of 50 taxa were identified in freshwater marsh, 20 in brackish marsh, and 12 in saline marsh. Freshwater marsh had 32 exclusive taxa but brackish and saline did not have any exclusive taxa. Furthermore, density, biomass, and diversity of aquatic macroinvertebrates in freshwater ponds were higher than in brackish and saline ponds. Variation in life history traits of macroinvertebrates and responses to environmental conditions (water depth, salinity) seem to be influenced macroinvertebrate assemblages across multiple marsh types.